The invention relates to the field of analog circuits.
In connection with control and drive circuits, it is often necessary to process an input current in such a way that an output current has a value which is proportional to the reciprocal value of the input current, while the product of the input and output current should be constant. Such a requirement is connected, for example, with the linearization of characteristic curves or control circuits for capacity diodes.
FIG. 1 shows a known circuit arrangement with which the desired coherence between the input current and the output current can be realized. The input current is supplied as an input signal to an input 1 of a multiplier device 2. The output 3 of the multiplier device 2 is compared in a control circuit 4 with a predetermined nominal signal. The nominal signal is applied via a non-inverting input 5 to the control circuit 4, while the output 3 of the multiplier device 2 is connected to an inverting input 6 of the control circuit 4. The result of the comparison at the output 7 of the control circuit 4 is applied as a second input signal via a further input 8 of the multiplier device 2. In the case of a deviation of the output 3 from the nominal signal, a control signal is generated by means of the control circuit 4, which control signal controls the multiplier device 2 in such a way that the control tracks the further input 8 until the product of the input signals of the multiplier device 2 corresponds to the nominal signal. The signal applied via the inverting input 6 to the control circuit 4 is then the output signal of the control circuit 4 which is combined with the input current in the desired manner.
It is an object of the present invention to provide an arrangement for forming a reciprocal value of an input current with simple circuit means.
According to the invention, this object is achieved by an arrangement for forming a reciprocal value of an input current, which arrangement comprises the following elements: a power supply source; a current source for generating a current for adjusting at least one operating point; a diode circuit with two devices operating as diodes, which are coupled in series; a transistor, in which a base of the transistor is coupled between the diode circuit and the current source and in which a collector of the transistor is coupled between the current source and the power supply source; and a further transistor, in which a base of the further transistor is coupled to an emitter of the transistor and an input current terminal and in which an emitter of the further transistor is connected to the input current terminal of the diode circuit and the power supply source in such a way that an output current flowing through the collector of the further transistor is proportional to the reciprocal value of the amount of an input current supplied via the input current terminal.
In the arrangement described, simple electronic components which can be manufactured in a cost-efficient way are used so that a circuit arrangement which can be manufactured with a small number of components at low cost is obtained for forming a reciprocal value of an input current which, in connection with different applications, can easily be used as an integrated circuit.
The diode circuit may be formed by two diodes or two transistors, the latter corresponding to the conventional realization of a diode function in integrated circuits. As regards the electrical properties and functions, both embodiments of the diode circuit are equivalent.
The implementation of the diode circuit by means of two transistors has the advantage of a better compensation of the temperature influence on component parameters due to identical behavior of similar components in the case of temperature changes.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.